Thermoplastic resins are widely used as materials for building construction, electric and electronic parts, household electric appliances, automobiles and fibers, because they are generally light, and excellent in water resistance, chemical resistance, electrical insulation and mechanical properties and are easy to mold.
Particularly, polycarbonate resins are widely employed as materials for housings of electric appliances, electronic office equipment such as computers, word processors and the like because of their excellence in mechanical properties, heat resistance and transparency, but the housings need high flame retardance in most cases from the viewpoint of safety.
Flame retardants have conventionally been incorporated into polycarbonate resins to make them flame retardant, but the desirable polycarbonate properties such as hardness, transparency, impact strength and rigidity are inevitably impaired due to flame-retardants incorporated therein. It is necessary to reduce to the minimum the deterioration of these desirable properties
JP-B-6-45747 (equivalent to U.S. Pat. No. 5,234,979) discloses a composition comprising a polycarbonate resin and a triaryl phosphate ester such as triphenyl phosphate and the like. However, the composition has not only low heat resistance but also a problem in appearance because of the migration of the triaryl phosphate ester to the surface of moldings thereof in the course of molding, i.e., blooming. JP-B-2-18336 discloses a composition comprising a polycarbonate resin and an oligomeric phosphate ester but it has reduced heat resistance due to the plasticizing effects of the oligomeric phosphate ester. Furthermore, International Patent Publication No. WO94/03535 (corresponding to U.S. Pat. No. 5,455,292) describes a specific oligomeric phosphate ester that lessens blooming, but the flame retardant and mechanical properties of the resultant compositions are not sufficient. A composition comprising a polycarbonate resin and a rubber reinforced resin, such as a rubber reinforced ABS resin or the like, is widely employed as a material for housings of electric appliances and electronic office equipment such as computers and word processors because of its excellence in mechanical properties and heat resistance, but the housings require high flame retardance in most cases from the viewpoint of safety. The impact strength of flame-retardant resins in the form of thin-walled moldings is also one of the important properties because they are frequently molded into more lightweight, thin-walled articles as electronic office equipment has become smaller and more portable with its remarkable progress.
In accordance with such demands, organic phosphorus compounds have been added to the compositions comprising the polycarbonate resins and the rubber reinforce resins such as ABS resins or the like for the purpose of imparting flame retardance thereto. For example, JP-A-2-32154 (equivalent to U.S. Pat. No. 5,061,745) discloses a composition comprising a polycarbonate resin, a rubber reinforced resin such as a rubber reinforced ABS resin or the like and a triaryl phosphate ester such as triphenyl phosphate. However, the composition has not only low heat resistance but also a problem in appearance because of the migration of the triaryl phosphate ester to the surface of moldings thereof in the course of molding, i.e., blooming. JP-A-2-115262 (equivalent to U.S. Pat. No. 5,204,394) discloses a composition comprising a polycarbonate resin, a rubber reinforced resin such as an ABS resin or the like and an oligomeric phosphate ester. However, the composition has the drawbacks of degradation in heat resistance due to the plasticizing effects of the oligomeric phosphate ester and blooming in the course of molding.
Furthermore, polyphenylene ether resins, which are excellent in mechanical properties, electrical properties, acid and alkali resistance and which are also low in water absorption and stable in dimensions, are widely used as materials for housings and chassis of electric appliances and electronic office equipment such as computers, word processors and the like. These housings require high flame retardance in most cases. The polyphenylene ether resins are excellent in flame retardance but inferior in processability, so that, in use, they are usually alloyed with styrene resins. As a result, their flame retardance deteriorates.
It has been known that a triaryl phosphate ester such as triphenyl phosphate, cresyl diphenyl phosphate, tricresyl phosphate, tris(isopropyl) phenyl phosphate and the like may be mixed as a flame retardant with the polyphenylene ether resins in order to improve their flame retardance, but the resultant polyphenylene ether resin compositions have defects such as deterioration of heat resistance and other properties and drawbacks such as volatilization, smoke emission and blooming of the incorporated phosphate ester in the course of molding.
To obviate the aforementioned defects and drawbacks, organic phosphate esters having larger molecular weight have been tried as flame retardants for practical use. For example, resorcinol tris(2,6-dimethylphenyl)phosphate is disclosed in EP-A-0007460, whereas resorcinol bis(diphenyl phosphate) of are disclosed in EP-A-0129824, EP-A-0129825, EP-A-0135726 and GB-A-2043083. Furthermore, tri(biphenyl) phosphate is disclosed in U.S. Pat. No. 4,683,255. However, these phosphate esters must be employed in large quantities for flame-retarding. According to our research findings, the resin compositions flame-retarded by incorporating these phosphate esters therein corrode molds during molding, the phosphate esters therein denature, the moldings thereof discolor and blister during molding or during a long time use and further the moldings deteriorate in electrical properties and flame retardance due to water absorption.
Thus, it has been impossible so far to provide the resin compositions which are simultaneously satisfactory in the flame retardance, performance and stability required of products. It is particularly necessary to further improve a balance of heat resistance and moldability of the flame-retardant resin compositions.